Apparatus and method for hydrostatic extrusion

ABSTRACT

Metal is placed under high hydrostatic pressure to increase its ductility and force it through an opening in a die. Control means is provided for controlling the extrusion rate.

United States Patent Zeitlin Jan. 28, 1975 [54] APPARATUS AND METHOD FOR 3,328,998 7/1967 s11111111'1'c1 111. .1 72/110 3395200 7/1968 Mucdcr, Jr. at ul. 425/66 HYDROSTATIC EXTRUSION [76] Inventor: Alexander Zeitlin, l8 Macy Avc.,

white Plains NY 10605 FOREIGN PATENTS OR APPLICATIONS 995,856 6/1965 Great Britain .1 72/272 [22] Flledl 271 1973 593,508 111/1947 010211 1311111111 1. 72/257 [2]] App]. N0.: 391,746

Related Application Dam Primary E.\'aminerRichz1rd J. Hcrbst [62] Division of Ser. No. 224,210, Feb. 7, 1972.

[52] U.S. Cl 72/9, 72/60, 72/257,

72/271 [57] ABSTRACT [51] Int. Cl. B2lc 31/00 [58] Field of Search 72/60, 257, 270-272, Metal is placed under high hydrostatic pressure to in- 425/66, 45 crease its ductility and force it through an opening in a die. Control means is provided for controlling the [56] References Cited extrusion rate.

UNITED STATES PATENTS 2,581,922 1/1952 Spencer 425/66 10 Claims, 14 Drawing Figures EXTRUSION AA. MACHINE PATENTED 3'. 862,557 sum 2 or s EXTRUSION A MACHINE PATENTED B I 3.862.557

SHEET 5 or 5 (88 V REL. AIR FIG. l3 COMPRESSOR 2l6 I :1: MLLAI'OR I80 QQ-i-l-Z-l-Z-E) r 5222222 :Z'LIII'IQ GHQ I I REL. f :i: V \TQ T\ m SIGNAL FROM DANCER AMPUFIED COMMAND FROM j E DANCER WARD LEONARD GENERATOR I- ma.

1: FIG. l4

MOTOR TO BE CONTROLLED APPARATUS AND METHOD FOR HYDROSTATIC EXTRUSION This is a division of application Ser. No. 224,210, filed Feb. 7, 1972.

BACKGROUND OF THE INVENTION This application pertains to the art of extrusion and more particularly to extrusion of metal into fine wire under high hydrostatic pressure.

Apparatus of a known type for hydrostatic extrusion of metals includes a high pressure chamber having an outlet opening through an extrusion die. Metal positioned in the pressure chamber is placed under very high hydrostatic pressure to increase its ductility and force it through the die opening. The wire is commonly tensioned by a pulling force as it exits through the die opening. Thus, the extrusion rate of the wire is a function of the pressure in the pressure chamber and of the pulling force on the wire. Variations in the pressure or the pulling force will change the extrusion rate. Many other variables affect the extrusion rate. For example, heat generated on the die surface during extrusion changes the coefficient of friction. The same effect takes place on the seals for a movable piston which provides pressurization for the pressure chamber. Changes in the temperature of the oil also change its viscosity. Fluctuations in the electric power supply will change the delivery pressure of the pump supplying hydraulic fluid to the movable piston.

Rapid increases in the extrusion rate may result in breakage of the wire due to its high acceleration rate and sudden deceleration when the extrusion rate decreases. Rapid decreases in the extrusion rate may cause the pulling force to exceed the breaking strength of the wire. It would be desirable to maintain the extrusion rate substantially constant so that a coiling device may coil the extruded wire at a constant rate which is the same as the extrusion rate.

SUMMARY OF THE INVENTION Apparatus of the type described includes control means for maintaining the extrusion rate of the wire substantially constant.

In accordance with one arrangement, mechanical augmentation drive means is connected with a movable piston for maintaining movement of the piston at a substantially constant rate despite fluctuations in hydraulic pressure or friction coefficients. In one arrangement, the mechanical augmentation drive means includes an elongated rod connected with the piston. The rod has threads formed thereon and a rotatable nut is threaded on the rod. The rotatable nut is in a fixed position so that it cannot move axially on the rod. A motor and gear arrangement rotate the nut at a substantially constant rate. Any tendency of the piston to speed up or slow down due to changes in such variables as coefficients of friction or hydraulic pressure is impeded by the mechanical augmentation drive.

In accordance with another arrangement, looping means is provided for tensioning and forming a loop in the extruded wire. The looping means includes automatically variable tensioning means for varying the tension in the wire responsive to changes in the length of the loop. This automatic change in the pulling force on the wire tends to maintain the extrusion rate substantially constant.

In another arrangement, the looping means for tensioning and forming a loop in the wire includes signal generating means responsive to changes in the length of the loop to control the extrusion rate.

It is a principal object of the present invention to provide an improved apparatus and method for hydrostatic extrusion of wire.

It is also an object of the present invention to provide such an apparatus with control means for extruding at a substantially constant rate.

It is a further object of the present invention to hydrostatically extrude wire at a substantially constant rate by monitoring the extrusion rate and varying at least one of the forces causing extrusion when changes in the extrusion rate occur.

It is an additional object of the present invention to provide a mechanical augmentation drive for maintaining movement of a piston at a substantially constant rate.

BRIEF DESCRIPTION OF THE DRAWING The invention may take form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawing which forms a part hereof.

FIG. 1 is an elevational cross-sectional view of a conventional hydrostatic extrusion apparatus with which the improvements of the present invention are utilized;

FIG. 2 is an elevational cross-sectional view of another conventional apparatus of the type with which the improvements of the present invention are utilized;

FIG. 3 is an elevational view of an improved variable tensioning device constructed in accordance with the present invention;

FIG. 4 is a cross-sectional elevational view looking generally in the direction of arrows 4-4 of FIG. 3;

FIG. 5 is a cross-sectional elevational view looking generally in the direction of arrows 5-5 of FIG. 3;

FIG. 6 is a diagram showing a circuit which includes signal generating means responsive to movements of a wire tensioning device;

FIG. 7 is a diagrammatic showing of another signal generating control device operated by a wire tensioning means;

FIG. 8 is a diagrammatic illustration of a primitive hydraulic system for supplying hydraulic pressure to the apparatus of FIGS. 1 and 2;

FIG. 9 is a diagrammatic illustration showing a motor control for use in the hydraulic circuit of FIG. 8;

FIG. 10 is a diagrammatic illustration of another hydraulic circuit;

FIG. 11 is a diagrammatic illustration of another hydraulic circuit;

FIG. 12 is a cross-sectional elevational view of a hydrostatic extrusion apparatus having a mechanical augmentation drive constructed in accordance with the present invention;

FIG. 13 is a diagrammatic illustration of a hydraulic circuit; and

FIG. 14 is a diagrammatic illustration of a circuit for controlling extrusion rate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows a hydrostatic extrusion apparatus A. Apparatus A includes a low pressure cylinder B and a smaller high pressure cylinder C. A piston D is slidably positioned in cylinder B and provided with suitable sliding seals as at 12. Piston D includes an elongated portion 14 extending through a closure 16 of cylinder B and suitably sealed as at 18. Portion 14 of piston D is connected with a much smaller piston E slidably positioned in cylinder C and provided with suitable sliding seals 22. Hydraulic-fluid supplied to cylinder B by a suitable pump acts against face 24 of piston D in the direction of arrows 26. This provides a pressure multiplier and the pressure of hydraulic fluid 28 in cylinder C is much greater than that in cylinder B. For example, the pressure in cylinder B may only be up to around 10,000 psi while the pressure in cylinder C may be as high as 500,000 psi. Piston E also provides a die having a die opening 30 therethrough in alignment with a larger bore 32 through piston D.,Pressure within bore 32 may be added to aid in maintaining metal ductile as it is extruded through die orifice 30. A slug of metal 34 positioned in cylinder C is subjected to extremely high hydraulic pressure to greatly increase its ductility and force it through orifice 30 in the form of a fine wire 36. A return line 38 for hydraulic fluid is provided for cylinder B.

In FIG. 2, hydrostatic extrusion apparatus F includes a low pressure cylinder G and a high pressure cylinder H. Low pressure cylinder G includes a cylindrical wall 42, and closures 44 and 46 suitably secured thereto, and provided with seals 48 and 50. Conduits 52 and 54 are connected with a hydraulic pump through suitable valves for supplying hydraulic pressure to low pressure cylinder G. A piston I is slidably positioned within cylinder G and provided with a peripheral sliding seal 56. A much smaller piston .I is slidably positioned within cylinder H and provided with a suitable peripheral sliding seal 58. Piston J is connected with piston I as by bolts 60 and slidably extends through sliding seal 62 in closure 46 of cylinder G. High pressure cylinder H has an opening 64. A die member 66 is positioned within cylinder H and is provided with a circular die opening 68 aligned with opening 64. A suitable peripheral seal 70 is provided for die 66. Supply of hydraulic fluid to cylinder G through line 52 results in hydraulic pressure acting on piston I in the direction of arrows 72. This force is concentrated on much smaller diameter of piston J so that the pressure of hydraulic fluid 28 within cylinder H is many times the pressure in cylinder G. The very high pressure within cylinder H increases the ductility of a metal mass 76 and forces the metal through die opening 68 so that it exits in the form of a very fine wire 78. Metal mass 76 may be in the form of a coiled rod or the like, or may simply be a slug.

FIG. 3 shows hydrostatic extrusion apparatus F and wire 78 exiting therefrom. It will be recognized that any type of extruding apparatus may be used with the features of the present invention. Wire 78 extends around a first idler pulley 82. Wire 78 then extends around another idler pulley 84 and is formed into an elongated U-shaped loop 86. Wire 78 then extends around another idler pulley 88 and is coiled on a coiling device K. Wire 78 and loop 86 extend around a pulley 90 of a dancer device L. In previous arrangements, device L simply consisted of a weighted pulley or roller as at 90 which merely hung in loop 86 for supplying a constant pulling force on wire 78. Increases or decreases in the extrusion rate due to changes in coefficients of friction or hydraulic pressure caused loop 86 to lengthen or shorten but the pulling force remained substantially constant.

In accordance with one arrangement, coiling device K includes a coiling drum 94 having a shaft 96 rotatably mounted in bearings 98 and 100. An electric motor M rotatably drives a fan 102 of a fan coupling which in turn drives fan member 104 on shaft 96 for rotating drum 94. Wire 78 may be coiled on drum 94 in a single layer so that a substantially constant torque is provided. A braking element 106 may be slidably positioned in bearings 108 and normally biased to the right in FIG. 4 by a coil spring 110. A solenoid coil 112 surrounding rod 114 connected with braking element 106 may be energized to move braking element 106 to the left in FIG. 4 so that braking element 106 will engage a side face of drum 94 to brake its rotation when loop 86 becomes smaller due to a decreasing rate of extrusion.

In accordance with one arrangement, dancer device L includes a pair of spaced-apart elongated members 116 suitably mounted to a stationary support. Members 116 have an elongated vertical slot 118 therein for slidably and rotatably receiving shaft 120 of pulley 90. Pulley and its shaft may move vertically up and down relative to support members 116 when loop 86 increases or decreases in size. A fork member 122 has arms 124 through which shaft 120 rotatably extends. A coil spring 126 is connected with fork member 122 at one of its ends and with a screw 128 at its other end. A nut 130 is threaded onto screw 128 and fixed to a support 132. Nut 130 may be rotatably attached in a fixed axial position to support 132 or may be nonrotatably fixed thereto. If nut 130 is rotatable, nut 130 may be rotated to move screw 128 axially therethrough to vary the force with which spring 126 pulls on fork member 122. If nut 130 is fixed, screw 128 may be rotated to move it axially through nut 130 and vary the force of spring 126. With the arrangement described, the force of spring 126 may be adjusted to a desirable value with loop 86 of a predetermined length. An increase in the extrusion rate of wire 78 will then increase the length of loop 86 and pulley 90 will move downward to decrease the pulling force of spring 126. This decrease in the pulling force on wire 78 will decrease the extrusion rate until it returns to its optimum value. A decrease in the desired constant extrusion rate will result in a shortening of loop 86 so that pulley 90 will move upward and the pulling force of spring I26 will increase so that the pulling force on wire 78 increases to increase the extrusion rate until it again reaches the desired rate.

The pulling force on wire 78 is limited due to the breaking strength of wire 78. Therefore, the pulling force is only 5 to 10 per cent of the total forces providing extrusion of wire 78 through the die opening. In some instances, the increase or decrease in pulling force provided by the device of FIG. 5 may be insufficient to vary the extrusion rate and bring it back to its proper value. Therefore, it may sometimes be desirable to provide a control impulse produced by movements of dancer device L for varying hydraulic pressure or other controllable conditions.

In one arrangement, as shown in FIG. 6, an electrical potential is supplied to a wire 136 positioned adjacent one of support members 116 by leads 138 and 140. An-

other electrical lead 142 is attached to shaft 120 of pulley 90 and a wiper 144 extends from shaft 120 to wire 136. Rising and falling movement of pulley 90 due to decreases and increases in the length of loop 86 will provide a variable voltage impulse to an electrical bridge 146 for indicating the deviation from a neutral position and produce a signal as by instrument 148 for correcting the hydraulic pressure and bring the extrusion rate back to its proper desirable value. The impulse provided by the electrical bridge may automatically be fed to the motor driving the hydraulic pump for automatically correcting the pressure. The same impulse may be used to operate the braking arrangement of FIG. 4.

In accordance with another arrangement, as shown in FIG. 7, an elongated iron pin 150 is connected with fork member 122 of dancer device I... Iron pin 150 extends through an electrical coil 152 which is divided into two sections 154 and 156. An alternating voltage is supplied to coil 152 through leads 158 and 160. An electrical bridge 162 is also connected across leads 158 and 160, and to the center of coil 152 by lead 164 through indicating instrument 166. In its neutral position, pin 150 provides a high permeability throughout entire coil 152. If the extrusion rate of wire 78 decreases, loop 86 will decrease in length and pull pin 150 upward. Coil 152 will then exert a downward pulling force on pin 150 to increase the pulling force on wire 78 and increase the extrusion rate. At the same time, the inductances in upper and lower portions 154 and 156 of coil 152 will no longer be equal and will require different voltages for the same current flow. This will produce a signal impulse through electrical bridge 162 and instrument 166 to indicate deviation from the desired extrusion rate.

As previously explained, the dancer arrangement provides for correcting the pulling force when extrusion rate deviates from its desired value. However, the pulling force is only a small fraction of the total force producing extrusion and it may be desirable to vary the hydraulic pressure for correcting the extrusion rate. FIG. 8 shows a primitive hydraulic system wherein hydraulic pump 170 is driven by an electric motor 172 for supplying hydraulic fluid from a reservoir 174 to low pressure cylinder G. Hydraulic fluid is pumped into cylinder G through either lines 52 or 54 by means of control valves 176 and 178. In one operating condition of valves 176 and 178, hydraulic fluid flows from pump 170 through conduit 180, valve 176 and conduit 52 to cylinder G. Hydraulic fluid returns from cylinder G on the bottom side of piston I through conduit 54, valve 178 and conduit 182. In the other operating condition of valves 176 and 178, hydraulic fluid flows through conduit 180, conduit 184, valve 178 and conduit 54 to low pressure cylinder G. Hydraulic fluid is returned from cylinder G at the top side of piston I through conduit 52, valve 176, conduit 186 and conduit 182.

As previously explained, the rate of extrusion is primarily a function of the hydraulic pressure acting on the coiled rod or slug of metal in high pressure chamber and the pulling force exerted on the extruded wire. It would appear that keeping the hydraulic pressure and the pulling force constant would produce a substantially constant extrusion rate. Unfortunately, this is not true because many other variables influence the rate of extrusion. Heat generated on the die surface changes the coefficient of friction and changes in oil temperature change viscosity. In addition, fluctuations in voltage applied to the motor driving the hydraulic pump influence the delivery pressure of the pump so that maintaining the hydraulic pressure constant is extremely difficult. One arrangement for controlling the output pressure of a positive displacement pump with fluctuations in line voltage is shown in FIG. 9. Ward- Leonard motor-generator set includes a motor 190 and a DC generator 192 having an externally controlled field 194. Monitoring the current in external field 194 makes it possible to vary the voltage delivered to pump motor 172 from zero to full value. The speed of motor 172 and pump can then be adjusted over a wide range. It is possible to use the control impulse generated with the dancer of FIGS. 6 or 7 for controlling the speed of motor 172 to control the delivery pressure of the pump. A Ward-Leonard control does not operate well near zero speed unless a gear reducer is introduced between motor 172 and pump 170. This makes it difficult to accurately control the output pressure of the. pump.

FIG. 10 shows a hydraulic arrangement wherein the delivery of pump 170 exceeds the demand at all times. The circuit is substantially the same as that of FIG. 8 except for the addition of throttling valve 198 in conduit and bleeder valve 202 in conduit 204 connected across conduits 180 and 182. Valves 198 and 202 may be controlled by solenoids 206 and 208 during a pressure stroke of piston I to extrude metal. Energizing of solenoids 206 and 208 during the pressure stroke opens valves 198 and 202. Valve 198 throttles the delivery of pump 170 and controls the volume of hydraulic fluid delivered to cylinder G. In the range of 0-20 per cent of maximum delivery, valve 198 is assisted by bleeder valve 202 which diverts back to reservoir 174 a portion of the hydraulic fluid passing through valve 198. This arrangement makes it possible to keep delivcry of the pump at a higher level than possible without any bleeder arrangement. The larger quantity of liquid results in a higher velocity throughout the hydraulic circuit. The higher velocity makes it possible to more accurately control the flow. The pressure in cylinder G can be monitored by means of a precision pressure gauge or by piezo-electric devices. One such arrangement is shown in FIG. 1 1 wherein a high precision pressure gauge 210 is connected through valve 212 with high pressure delivery conduit 180.

Another arrangement for the hydraulic circuit is shown with reference to FIG. 13. The circuit is essentially the same as that described with reference to FIGS. 10 and 11. In addition, a hydropneumatic accumulator 216 is installed in conduit 180. A relief valve 218 is provided for relieving accumulator 216. Hydraulic pressure can be adjusted by adjusting the air pressure in accumulator 216 by operating air compressor 220 and bleed valve 218. Adjustment of operating pressure during extrusion may be made by monitoring impulse signals transmitted from the dancer arrangements described with reference to FIGS. 6 and 7. A system of this type produces relatively satisfactory results except for the fact that there is a time delay of several seconds while adjustment takes place.

All hydraulic systems have some elasticity which makes it a practical impossibility to provide instantaneous response to controls. Measurement of pressures is also difficult and accurate control of pressure requires some time delay. The high friction between the wire being extruded and the die opening, and friction between the pistons and the walls of the cylinders, also result in sticking of the system at low extrusion rates. One arrangement for adjusting the rate of displacement of piston I in cylinder G, and therefore the rate of displacement of piston J in cylinder l-I, includes a mechanical augmentation drive which by-passes the difficult measurement and time delay problems previously mentioned. One such arrangement is shown with reference to FIG. 12. A rod 226 is attached to piston I as by bolts 228 and extends through an opening in closure 44 which is suitably sealed as at 230. Rod 226 has threads 232 formed thereon and is threaded through a rotatable nut 234 which is rotatably mounted to suitable supports 236 in a fixed axial position. The outer periphery of nut 234 is formed as a worm wheel 238 engaging a worm gear 240 which is suitably driven through a gear reduction by an electric motor. With the hydraulic pressure in cylinder G and the pulling force on wire 78 adjusted to proper values for extruding wire 78 at a substantially constant predetermined rate, the motor driving worm gear 240 is also adjusted for rotating nut 234 to advance rod 226 at the same rate as piston 1. During normal operation, when wire is being extruded at the substantially constant predetermined rate, nut 234 is simply idling. However, an increase or decrease in the desirable constant extrusion rate will result in nut 234 acting positively to retard or increase the movement of piston I so that the desirable constant extrusion rate will be maintained. It will be recognized that it is also possible to adjust the motor driving worm gear 240 by using impulses from the dancer arrangements described with reference to FIGS. 6 and 7.

With reference to FIG. 14, the impulse signal provided by the dancer arrangements of FIGS. 6 or 7 is sent by leads 250 and 252 to a bridge circuit 254 and hence through an amplifying triode 256, and then to an additional positive or negative exciter 258. This signal is then used to control the Ward-Leonard motorgenerator described with reference to FIG. 9. The motor-generator control then controls either the motor driving the hydraulic pump or the motor driving the worm gear in the mechanical augmentation drive system of FIG. 12. In the preferred arrangement, an anticipatory type of control is used. Such a control not only monitors changes in the quantity being measured, but also the rate of such changes. Such a control not only takes into account the amount of deviation from the desired value but also considers the first derivative. For example, if the dancer begins movement from its neutral position at a fast rate, the monitoring circuit provides a fast response. However, as the motion of the dancer slows down and ultimately reverses, an anticipatory monitoring device will anticipate such a change and reduce the commanded action without danger of over controlling or hunting. Such controls are wellknown to those skilled in the art and several types are discussed in a handbookentitled Process Instruments and Controls Published by McGraw-I-Iill. Pages 11-16 through 11-40 of the article entitled Fundamentals of Automatic Processed Control by George A. Hall, Jr. particularly describe such controls. A derivative mode anticipatory control is described on page 11-25 and a more sophisticated three-term mode on page 11-26. The subject matter of this article is hereby incorporated herein by reference.

Although the invention has been described with reference to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications and is limited only by the scope of the claims.

Having thus described my invention, 1 claim 1. Apparatus for cold extruding metal into a fine wire comprising: an extrusion die, hydraulic pressure means for forcing said metal through said die to form a fine wire, looping means for tensioning and forming a loop in said wire, said looping means including signal generating means responsive to change in length of said loop and the rate of said change, and loop tensioning means responsive to said signal generating means for applying a higher tensioning force to said loop in response to decrease in the length of said loop, and applying a lower tensioning force to said loop in response to increase in the length of said loop.

2. In a method for cold extruding fine wire by hydrostatically forcing metal through a die the steps comprising: tensioning and forming a loop in said extruded wire; monitoring the change and rate of change of the length of said loop; and automatically varying the tension in said wire responsive to said change and rate of change.

3. Apparatus for extruding metal into a fine wire through a die opening at substantially constant rate comprising: hydraulic pressure means including movable piston means for generating extruding pressure, mechanical augmentation drive means connected with said piston for augmenting said hydraulic pressure means to move said piston at a rate for maintaining extrusion of said wire at a substantially constant rate, and control means for determining the extrusion rate of said wire through said die opening to control and vary the speed of said mechanical augmentation drive means for maintaining the extrusion rate of said wire at a substantially constant rate, wherein said control means includes looping means for tensioning and forming a loop in said wire, said looping means including signal generating means responsive to changes in the length of said loop to control and vary the speed of said mechanical augmentation drive means for maintaining the extrusion rate of said wire substantially constant.

4. The apparatus of claim 3 wherein said signal generating means is responsive to both changes in length of said loop and the rate of change in length of said loop.

5. Apparatus for extruding metal into a fine wire through a die opening at substantially constant rate comprising: hydraulic pressure means including movable piston means for generating extruding pressure, constant speed mechanical control means connected with said piston for controlling said hydraulic pressure means to move said piston means at a substantially constant rate, looping means for forming a loop in said wire as said wire is extruded through said die opening and for tensioning said wire for pulling said wire through said die opening, said looping means including automatically variable tensioning means for varying the pulling force on said wire in response to changes in the length of said loop to maintain the extrusion rate of said wire through said die opening substantially constant.

6. The apparatus of claim 5 wherein said looping means includes spring means for tensioning said wire.

said spring means having a variable spring rate for applying a higher tensioning force to said loop in response to decrease in the length of said loop and for applying a lower tensioning force to said loop in response to increase in the length of said loop.

7. The apparatus of claim wherein said looping means is anticipatory of the rate of change in the length of said loop for varying the tensioning force on said wire for maintaining the extrusion rate of said wire through said die opening substantially constant.

8. A method for extruding metal into a fine wire through a die opening at a substantially constant rate comprising the steps of: applying hydraulic pressure to said metal by means of hydraulically actuated movable piston means for forcing said metal through said die opening as a fine wire at a substantially constant rate, monitoring the extrusion rate of wire through said die opening, and mechanically controlling and varying the advancement rate of said piston means in accordance with the monitored extrusion rate for maintaining the extrusion rate of wire through said die opening substantially constant, wherein said step of monitoring the extrusion rate of said wire is carried out by forming said wire into a loop and tensioning said wire, and generating signals in response to changes in the length of said loop to mechanically control and vary the advancement rate of said piston for maintaining the extrusion rate of said wire through said die opening substantially constant.

9. A method for extruding metal into a fine wire through a die opening at a substantially constant rate comprising the steps of: applying hydraulic pressure to said metal by means of hydraulically actuated movable piston means for forcing said metal through said die opening as a fine wire at a substantially constant rate, mechanically controlling the advancement rate of said piston for maintaining the advancement rate of said piston substantially constant, forming a loop in said wire and tensioning said wire to pull said wire through said die opening, and automatically varying the tension in said wire in response to changes in the length of said loop for maintaining the extrusion rate of said wire through said die opening substantially constant.

10. The method of claim 9 and including the step of anticipating changes in the length of said loop for varying the tension in said wire. 

1. Apparatus for cold extruding metal into a fine wire comprising: an extrusion die, hydraulic pressure means for forcing said metal through said die to form a fine wire, looping means for tensioning and forming a loop in said wire, said looping means including signal generating means responsive to change in length of said loop and the rate of said change, and loop tensioning means responsive to said signal generating means for applying a higher tensioning force to said loop in response to decrease in the length of said loop, and applying a lower tensioning force to said loop in response to increase in the length of said loop.
 2. In a method for cold extruding fine wire by hydrostatically forcing metal through a die the steps comprising: tensioning and forming a loop in said extruded wire; monitoring the change and rate of change of the length of said loop; and automatically varying the tension in said wire responsive to said change and rate of change.
 3. Apparatus for extruding metal into a fine wire through a die opening at substantially constant rate comprising: hydraulic pressure means including movable piston means for generating extruding pressure, mechanical augmentation drive means connected with said piston for augmenting said hydraulic pressure means to move said piston at a rate for maintaining extrusion of said wire at a substantially constant rate, and control means for determining the extrusion rate of said wire through said die opening to control and vary the speed of said mechanical augmentation drive means for maintaining the extrusion rate of said wire at a substantially constant rate, wherein said control means includes looping means for tensioning and forming a loop in said wire, said looping means including signal generating means responsive to changes in the length of said loop to control and vary the speed of said mechanical augmentation drive means for maintaining the extrusion rate of said wire substantially constant.
 4. The apparatus of claim 3 wherein said signal generating means is responsive to both changes in length of said loop and the rate of change in length of said loop.
 5. Apparatus for extruding metal into a fine wire through a die opening at substantially constant rate comprising: hydraulic pressure means including movable piston means for generating extruding pressure, constant speed mechanical control means connected with said piston for controlling said hydraulic pressure means to move said piston means at a substantially constant rate, looping means for forming a loop in said wire as said wire is extruded through said die opening and for tensioning said wire for pulling said wire through said die opening, said looping means including automatically variable tensioning means for varying the pulling force on said wire in response to changes in the length of said loop to maintain the extrusion rate of said wire through said die opening substantially constant.
 6. The apparatus of claim 5 wherein said looping means includes spring means for tensioning said wire, said spring means having a variable spring rate for applying a higher tensioning force to said loop in response to decrease in the length of said loop and for applying a lower tensioning force to said loop in response to increase in the length of said loop.
 7. The apparatus of claim 5 wherein said looping means is anticipatory of the rate of change in the length of said loop for varying the tensioning force on said wire for maintaining the extrusion rate of said wire through said die opening substantially constant.
 8. A method for extruding metal into a fine wire through a die opening at a substantially constant rate comprising the steps of: applying hydraulic pressure to said metal by means of hydraulically actuated movable piston means for forcing said metal through said die opening as a fine wire at a substantially constant rate, monitoring the extrusion rate of wire through said die opening, and mechanically controlling and varying the advancement rate of said piston means in accordance with the monitored extrusion rate for maintaining the extrusion rate of wire through said die opening substantially constant, wherein said step of monitoring the extrusion rate of said wire is carried out by forming said wire into a loop and tensioning said wire, and generating signals in response to changes in the length of said loop to mechanically control and vary the advancement rate of said piston for maintaining the extrusion rate of said wire through said die opening substantially constant.
 9. A method for extruding metal into a fine wire through a die opening at a substantially constant rate comprising the steps of: applying hydraulic pressure to said metal by means of hydraulically actuated movable piston means for forcing said metal through said die opening as a fine wire at a substantially constant rate, mechanically controlling the advancement rate of said piston for maintaining the advancement rate of said piston substantially constant, forming a loop in said wire and tensioning said wire to pull said wire through said die opening, and automatically varying the tension in said wire in response to changes in the length of said loop for maintaining the extrusion rate of said wire through said die opening substantially constant.
 10. The method of claim 9 and including the step of anticipating changes in the length of said loop for varying the tension in said wire. 